1. Field of the Invention
The present invention relates to a method of detecting and controlling a work start point of a robot having an interpolating function and a response function to a position sensor.
2. Description of the Related Art
In order to teach playback type robots, a work object must be positioned with a high degree of accuracy so that the locus of the edge of the robot end effector (which has the same meaning as "work tool" hereinafter described) as taught coincides with the work line of a work object. When there is a variation in dimensional accuracy of the work object itself or when the work object is not properly positioned, the robot cannot be worked in accordance with the locus data taught. To solve this problem, robots equipped with a position error detecting sensor have recently been studied and developed, and some of these have already been put into practical use.
As this sensor, various kinds of sensors such as the mechanical type, magnetic type, arc sensor type in which the arc itself is used as an information source, and optical type have been proposed. However, the mechanical type has various drawbacks which are caused because of contact with the object. The magnetic type also has various drawbacks in that the sensor must be arranged near the robot end effector in terms of detection sensitivity. The arc sensor type has the drawback that a high precision cannot be obtained due to variations in welding condition and due to the characteristics of the welding arc itself.
The optical type, however, is excellent in that the shape of the operating work piece can be recognized. In the optical type, a system in which an image signal is obtained due to the reflection of an external light emitting source (e.g., laser slit light) can recognize the line of the work point of the operating workpiece. However, this system has the following drawbacks because the work tool and the work line are relatively positioned based on the assumption that the relative position of the sensor and the working tool never changes. In other words, if the working tool itself deforms or if play, deformation, or deviation of the mechanism to which the sensor is attached occurs, the relative position between the sensor and the work point of the work tool changes, so that they cannot be accurately positioned for the operating work piece. When this point is considered with respect to production technology, the deviation of the operating work piece side is equivalent to the deviation of the robot side including the deviation of the sensor as well. An automated system using a position correcting sensor robot which is constructed on the assumption that all of the robot, sensor, and operating work piece deviate from the normal positions is excellent in terms of production technology, as compared with one using a position correcting sensor robot which is constructed on the assumption that the relative position between the robot and the sensor never changes but the operating work piece deviates from the normal position. With respect to this viewpoint, it is obvious that a sensor system which directly recognizes the relative position between the working tool and the operating work piece is far superior to a sensor system which recognizes only the position of the operating work piece due to the reflection of the external light emitting source.